Articulating trailing tag axle

ABSTRACT

First hydraulic drives (e.g. cylinders, pistons) and lift arms attached to dump truck side panels, preferably reinforced, move a trailing tag axle, and wheels supported by the tag axle, between operative and storage positions without bending the truck frame. A linkage assembly and second hydraulic drives (e.g. cylinders, pistons) coupled to the lift arms and the first hydraulic drives move the tag axle and the wheels between raised and lowered positions. In the operative positions of the lift arms and the tag axle, the wheels contact the ground and, because of the first hydraulic drive construction, move smoothly over road bumps and into road dips. In their storage position, the lift arms are disposed above and to the rear of the dump truck with the trailing tag axle and the wheels above the body but lowered to minimize their height above the truck. With the lift arms and the tag axle in the storage position, the second hydraulic drives initially the tag axle, and then the first hydraulic drives more the lift arms, to move the tag axle to the operative position. With the lift arms and the trailing tag axle in the operative position, the lift arms, and the tag axle, are moved to position the tag axle at the storage position. With the lift arms and the tag axle in the storage position, the truck load can be dumped without obstruction. Furthermore, the force for moving the tag axle is minimal when the lift arms are in the storage position.

This application is a continuation of application Ser. No. 08/365,838,filed Dec. 29, 1994, now U.S. Pat. No. 5,823,629.

This invention relates to a trailing tag axle for attachment to a dumptruck to increase the load that the dump truck can legally carry whiletravelling along a road. More particularly, the invention relates to atrailing tag axle which is attached to a dump truck to provide a maximalload in the dump truck during the movement of the dump truck along aroad and to provide for a dumping of the load from the dump truckwithout any obstruction when the dump truck reaches its destination.

Dump trucks have been in use for many years. The dump trucks have aframe and a hollow body disposed on the frame. A tailgate is disposed onthe body at the rear end of the body and is movable between a closedposition and an open position. In the closed position, the tailgatedefines an enclosure with the body to retain the load in the body. Inthe open position, the tailgate opens the rear end of the dump truck toprovide for the dumping of the load from the body. To facilitate thedumping of the load from the body, the front of the body may be tiltedupwardly relative to the frame so that the load will flow by gravityfrom the rear end of the body.

Truckers always desire to carry the maximum load possible. However, thetruckers have been restricted by governmental regulations in the amountof load that the trucks can carry. These restrictions have been providedto prevent the road or bridge from becoming damaged, such as bycracking, as a result of the imposition of excessive loads on the roador bridge. The governmental restrictions have been based upon thelongitudinal distance between the front and rear wheels in the dumptruck. As will be appreciated, the maximum load imposed by governmentalregulations in a dump truck can be increased in accordance withincreases in the distance between the front and rear.

In order to increase the weight of the load capable of being carried bya dump truck, trailing tag axle assemblies have been attached to thedump trucks at the rear ends of the dump trucks. Each trailing tag axleassembly has a trailing tag axle at the rear end of the assembly. Wheelsare attached to the trailing tag axle. In one position of the trailingtag axle assembly, the wheels are disposed on the road. This increasesthe effective length over which the weight of the load in the dump truckcan be distributed. As a result, the dump truck can move along the roadwith an increased load weight without damaging the road or bridge.

When the dump truck reaches its destination, the dump truck body ispivoted in a direction relative to the frame so that the front end ofthe body is raised relative to the rear end of the frame. The tailgateis concurrently raised to open the truck body at the rear end of thetruck body so that the load in the truck body can become deposited bygravity on the ground or in one of many types of road equipment (i.e.spreaders, wideners, etc.). Concurrently with the opening of thetailgate (or preferably before the tailgate is opened and the body israised), the trailing tag axle assembly is raised so that the loaddropping to the ground will not cover the tag axle assembly. It isundesirable for several reasons for the load to flow on the tag axleassembly. For example, the load may damage the trailing tag axleassembly. Furthermore, the load may be sticky so that it becomes bonded,sometimes permanently, to the trailing tag axle assembly. This mayinhibit any proper operation of the trailing tag axle assemblysubsequently.

There are several disadvantages to the trailing tag axle assemblies nowin use. One disadvantage is that the trailing tag axle is generallyattached to the frame of the truck chassis. Because of this, there is atendency for the chassis frame to become bent or buckled when thetrailing tag axle assembly is in the operative (or lowered) position.The bending or buckling of the dump truck frame has limited the life ofthe dump truck. To overcome this, the frame has sometimes beenstrengthened. However, this has increased the weight of the dump truckand has limited the weight of the load that can be added to the truck bythe inclusion of the trailing tag axle assembly.

Another disadvantage to the trailing tag axle assemblies now in use hasbeen that the tag axle assemblies obstruct the flow of the load from thetruck body when the front of the truck body has been pivoted upwardlyand the tailgate has been opened. This has resulted from the fact thatthe trailing tag axle assembly has been attached to the frame at anintermediate position between the opposite lateral sides of the frame.Thus, the attachment of the trailing tag axle assembly to the frameobstructs the flow of the load from the truck body even when thetrailing tag axle assembly is raised.

There are also other significant disadvantages to the trailing tag axleassemblies now in use. This partially results from the fact that theheight of the trailing tag axle assembly in the raised position exceedsgovernment regulations when the trailing tag axle assembly is attacheddirectly to the rear end of the frame. To overcome this governmentalregulation, the length of the trailing tag axle assembly has beenshortened, or the truck frame has been extended to the rear of thetruck. However, shortening the trailing axle assembly has reduced theamount of the additional weight that can be carried by the dump truck asa result of the addition of the trailing tag axle assembly an dextending the truck frame has made it difficult or impossible to dumpinto some types of paving equipment.

Another significant disadvantage exists in the trailing tag axleassemblies now in use. Thus results from the inability of the trailingtag axle assembly to respond smoothly and efficiently to bumps and dipsin the road while the wheels on the trailing tag axle are disposed onthe road and the dump truck is travelling along the road. This hasaffected the smoothness in the ride of the dump truck while the dumptruck is travelling along the road. This has also affected the life oftrailing axle assemblies now in use. This results from the fact that, asthe truck travels through a dip in the road, the forces and stresses onthe trailing axle assembly are significantly increased.

Another disadvantage in the dump trucks now in use has been that thesupport structure for the trailing tag axle assembly extends from therear end of the dump truck. Under some circumstances, this mayconstitute a dangerous appendage that does not conform to governmentregulations. A further disadvantage has been that the trailing tag axleassemblies have had to be raised in order for the dump truck to back up.

This has caused the dump truck to be overweight during such backing-upmovement and to exceed governmental regulations when the load in thedump truck has been increased because of the attachment of the trailingtag axle assembly. A further disadvantage has been that the appendagesof the prior art have made it difficult or even impossible to dump aload into some types of paving machines.

This invention provides a trailing tag axle assembly which overcomes thedisadvantages specified above. The trailing tag axle assembly isattached to the truck body such that the truck frame does not bend orbuckle away from the body even when the trailing tax axle assembly israised or lowered. The trailing tag axle assembly is attached to theside panels of the dump truck so that the full length of the tag axleassembly can be used in distributing the weight of the load in the dumptruck. The tag axle assembly does not obstruct the flow of the load fromthe dump truck in the raised position of the trailing tag axle assembly.Furthermore, the effective length of the trailing tag axle assembly isshortened in the raised position of the trailing tag axle assembly sothat the height of the tag axle assembly is within governmentalregulations. The trailing tag axle assembly is also constructed torespond smoothly and efficiently to bumps and dips in the road while thedump truck is travelling along the road. This results from the fact thatthe force variations are minimized as the truck travels through bumpsand dips in the road. In one embodiment, the dump truck can be moved inreverse with the wheels of the trailing tag axle assembly disposed onthe road, thereby providing for the operation of the dump truck withingovernmental regulations.

In one embodiment of the invention, first hydraulic drives (e.g.cylinders, pistons) and lift arms attached to side panels, preferablyreinforced, of a dump truck move a trailing tag axle between operativeand storage positions without bending the truck frame. A linkageassembly and second hydraulic drives (e.g. cylinders, pistons) coupledto the lift arms and the trailing tag axle move the trailing tag axle,and wheels supported (preferably pivotably) by the trailing tag axle,between operative and storage positions.

In the operative position of the lift arms and the trailing tag axle,the wheels contact the ground and, because of the first hydraulic driveconstruction, move smoothly over bumps and into dips in the road. In thestorage position of these members, the lift arms are disposed above thedump truck with the trailing tag axle and the wheels lowered relative tothe lift arms to minimize their height above the truck.

With the lift arms and the trailing tag axle in the storage position,movement is initially provided by the second hydraulic drives to thetrailing tag axle, and then by the first hydraulic drives to the liftarms, to move the tag axle to the operative position. With the lift armsand the tag axle in the operative position, movements are initiallyprovided to the lift arms and then to the tag axle to position the tagaxle at the storage position. When the lift arms and the tag axle are inthe storage position, the load in the truck can be dumped without anyobstruction. Furthermore, the force for moving the tag axle is minimalwhen the lift arms are in the storage position.

In the drawings:

FIG. 1 is a side elevational view of a dump truck and a tag axleassembly constituting one embodiment of this invention, the tag axleassembly being shown as being attached to the dump truck and disposed inthe extended position with wheels in the tag axle assembly disposed onthe ground;

FIG. 2 is a sectional view of the dump truck and the tag axle assemblysubstantially on the line 2--2 of FIG. 1 and shows the tag axle assemblyin a lowered position;

FIG. 3 is an enlarged perspective view of the tag axle assembly shown inFIGS. 1 and 2 and of the rear end of the dump truck with the tag axleassembly attached to the dump truck and with the wheels in the tag axleassembly disposed on the ground;

FIG. 4A is a sectional view taken substantially on the line 4--4 of FIG.2 and shows the tag axle assembly in the raised position relative to therear of the dump truck, with the tag axle and the wheels on the tag axlelowered to minimize the vertical height of the tag axle assembly abovethe ground;

FIG. 4B is a sectional view taken substantially on the line 4--4 of FIG.2 and shows the tag axle and the wheels pivoted to a raised positionfrom the lowered position shown in FIG. 4A;

FIG. 4C is a sectional view taken substantially on the line 4--4 of FIG.2 and shows in solid lines the position of the tag axle assemblyrelative to the rear of the dump truck with the wheels in the tag axleassembly on the ground and also shows the tag assembly in broken linesat a position between the positions shown in FIG. 4B and in solid linesin FIG. 4C;

FIG. 5A is an enlarged side elevational view of the tag axle assembly inthe position also shown in FIG. 4A;

FIG. 5B is an enlarged side elevational view of the tag axle assembly ina position between the position shown in FIGS. 4A and 5A and theposition shown in FIG. 4B;

FIG. 5C is an enlarged side elevational view of the e tag axle assemblyat a position between the position shown in FIG. 5B and the positionshown in FIG. 4B;

FIG. 5D is an enlarged side elevational view of the tag axle assembly inthe position also shown in FIG. 4B;

FIG. 6 is an enlarged perspective view of the rear end of the dumptruck, of a tailgate at the rear end of the tag axle assembly and of thetag axle assembly in the raised position and shows a portion of thetailgate broken away;

FIG. 7 is a sectional view, taken substantially on line 7--7 of FIG. 6,of apparatus for opening the tailgate to provide for the dumping of theload in the dump truck;

FIG. 8 is a schematic diagram of the electrical circuitry which is usedin conjunction with the tag axle assembly shown in the previous figuresto provide a movement of the tag axle assembly between the operative andstorage positions; and

FIG. 9 is a schematic diagram of the hydraulic circuitry which is usedin conjunction with the trailing tag axle assembly shown in the previousFigures to provide a movement of the trailing tag axle assembly betweenthe operative and storage positions;

FIG. 10 is a side elevational view of the dump truck and the trailingtag axle assembly with the trailing truck body pivotably raised at thefront end relative to the truck frame to provide for a dumping of theload in the truck body;

FIG. 11 is a perspective view of the trailing tag axle assembly and shows features in the trailing tag axle assembly for providing a smoothand efficient movement of the wheels on the trailing tag axle over bumpsand into dips in the road while the dump truck is travelling along theroad.

In one embodiment of the invention, a dump truck generally indicated at10 (FIGS. 1 and 3) is provided with a cab 12, a frame 14, a truck body16 and side panels 18, the side panels defining the lateral extremitiesof the truck body. The side panels 18 may be reinforced for the purposesof this invention. A tailgate 20 may be provided at the rear end of thedump truck 10. The tailgate 20 may be movable between a closed positionand an open position. In the closed position, a load in the truck body16 is prevented from leaving the truck body. In the open position of thetailgate 20, the load in the truck body 16 is able t o leave the truckbody through the rear end of the truck body. The flow of the load fromthe truck body 16 is facilitated by pivoting the front end of the truckbody upwardly on a plurality of collapsible stanchions, generallyindicated at 22 in FIG. 10, the fulcrum being near the rear end of thedump truck. The construction of the dump truck as described above may beconsidered to be known in the art except for the reinforced side panels18.

A trailing tag axle assembly generally indicated at at 24 (FIGS. 1 and3) is attached to the side panels 18 at the rear end of the dump truck.The tag axle assembly includes first hydraulic drives generallyindicated at 26. The hydraulic drives 26 may include hydraulic cylinders28 pivotably attached to the side panels 18 at the rear of the sidepanels in terminate the height of the side panels. The first hydraulicdrives 26 also include hydraulic rods 30 disposed with in the cylinders28 at on e end and attached at is the other end to lift arms 34. Liftarms 34 are pivotably attached at one end to pivot pins 36 on the sidewalls 18 and at the other end to the link age assembly 32.

The attachment of the lift arms 34 and the cylinders 28 to the sidepanels 18 of the dump truck 10 rather than to the frame 14 offerscertain advantages. The side panels 18 have a large area between thefront and rear of the dump truck 10. Because of this, any weight imposedby the hydraulic drives 26 and the lift arms 34 and by the t railing tagaxle assembly 24 attached to the hydraulic drives and the lift arms isdistributed over the wide areas provided by the side panels 18. As aresult, the frame 14 does not become bent or bowed away from the body 16when the hydraulic drive means 26 and the lift arms 34 are pivotedbetween raised and lowered positions.

The cylinders 28 are filled with hydraulic oil. As shown in FIG. 11, therods 30 are preferably hollow. Closed hollow pistons 38 are disposedwithin the rods 30 and are filled with a suitable hydraulic oil 40. Asuitable gas 42 such as nitrogen is disposed in the rods 30 to the rearof the pistons 38. The gas 42 in the rods 30 communicates throughconduits 44 with gas 46 such as nitrogen in an accumulator, generallyindicated at 48, which is included in the linkage assembly tube on theend of the lift arms 34. The accumulator 48 is inside a support tube 49which supports brackets 50 at its opposite ends. The brackets 50 on theends of the lift arms 34 have pins 52 which receive the rods 30 forpivotable movement.

A pair of brackets 56 (FIG. 3) are attached to the support tube 49 atspaced positions near the middle of the support tube. Disposed in thearea between the brackets 56 is a second pair of brackets 60. A pin 62attached to the brackets 56 extends through the brackets 56 and 60 tosupport a pair of arms 66 at one end of the arms. The arms 66 areattached at the other end to a beam 68 which is in turn attached to anaxle 70. Wheels 72 are suitably disposed on the axle 70.

A short linkage 74 is pivotably mounted at one end on the brackets 60.At its opposite end, the short linkage 74 is pivotably attached as bybrackets 76 and pivot pins 78 to one end of a long linkage 80. Theopposite end of the long linkage 80 is pivotably mounted as at 82 to apair of spaced brackets 84 which are supported by the arms 66. A secondhydraulic drive generally indicated at 86 (FIGS. 5B-5D) is provided topivot the linkages 74 and 80 relative to each other. The secondhydraulic drive 86 includes a piston 88 pivotably attached to the longlinkage 80 as at 90 and also includes a cylinder 92 pivotably attachedas at 94 to the beam 68.

The trailing tag axle 70 has three (3) different positions as shown inFIGS. 4A-4C. In one of these positions (FIGS. 1, 3 and 5D), the trailingtag axle 70 is disposed as shown in FIG. 1 such that the wheels 72 aredisposed on the ground. In this position, the longitudinal distancebetween the front wheels 96 on the dump truck 10 and the wheels 72 isconsider ably increased relative to the distance between the frontwheels 96 and the rear wheels 98 on the dump truck. Because of thissignificant increase in the longitudinal distance when the wheels 72contact the ground, the load carried in the truck body 16 can beconsiderably increased while the dump truck is travelling along a road.

The trailing tag axle 70 has a second position in which the trailing tagaxle is disposed above the dump truck. This is shown in FIG. 4A. Whenthe trailing tag axle 70 is disposed above the dump truck 10, thetailgate 20 can be opened to provide for the dumping of the load in thetruck body 16. As will be seen in FIG. 6, the linkage assembly 32 isdisposed above the truck body 16, and the hydraulic drives 26 and thelift arms 34 are disposed at the opposite lateral ends of the truck body16. As a result, the opening at the rear end of the truck body 16 withthe tailgate 20 open is not obstructed in any way so that the load inthe truck body is able to flow freely out of the truck body to theground. The flow of the load out of the truck body to the ground isfacilitative by tilting the e front end of the truck body 16 ontelescopic stanchions 22 as shown in FIG. 10.

The trailing tag axle 70 and the wheels 72 are shown in a third positionin FIGS. 4B and 5D. This position occurs after the rod 30 has beencontracted into the cylinder 28 to raise the hydraulic drives 26 and thelift arms from the operative position shown in FIGS. 1 and 3 to thestorage position shown in FIGS. 4A, 4B, and 6. However, as shown in FIG.4B, the axle 70 and the wheels 72 extend a significant is distance abovethe hydraulic drives 26 and the lift arms 34. This is undesirable inview of governmental restrictions that limit the height of trailing tagaxle assemblies above the ground. These governmental restrictions arepartially imposed to provide free passage of the dump trucks throughunderpasses of bridges when the dump trucks are travelling with a lightload or no load and with the hydraulic drives 26 and the lift arms 34raised.

The trailing tag axle 70 and the wheels 72 are shown in FIGS. 4A and 5Ain a position corresponding to the second position described above. Inthis position, the trailing tag axle 72 and the wheels 70 have beenretracted downwardly from the position shown in FIGS. 4B and 5C. In theposition shown in FIGS. 4A and 5A, the height of the trailing tag axle70 and the wheels 72 above the truck body 16 is minimized. In this way,the trailing tag axle assembly 24 of this invention is able to meetgovernmental regulations. Furthermore, the trailing tag axle assembly 24is protected in this position since it is disposed forwardly above thetruck body 16. When the trailing tag axle assembly 24 is in thisposition, it does not interfere with the dumping of the load into roadequipment.

When the trailing tag axle 70 and the wheels 72 are in the positionshown in FIGS. 4A and 5A, the center of gravity of the trailing tag axleand the wheels and the associated members such as the hydraulic drivemeans 86 and the linkages 74 and 80 is relatively close to the pivotpoint of the hydraulic drive means 86. This tends to minimize the forcerequired to be provided by the hydraulic drive means 86 to move the tagaxle 70 and the wheels 72 from the position shown in FIGS. 4A and 5A tothe position shown in FIGS. 4B and 5D.

When the dump truck is dumping its load, the trailing tag axle 70 andthe wheels 72 are in the position shown in FIGS. 4A and 5A. To positionthe axle 70 so that the wheels 72 contact the ground, the secondhydraulic drive 86 is operated to extend the piston 88 from the cylinder92. This is shown progressively in FIGS. 5A, 5B, 5C and 5D. As thepiston 88 is extended from the cylinder 92, the long linkage 80 ispivoted relative to the short linkage 74 so that the short linkage andthe long linkage becomes progressively aligned relative to each other.When the long linkage 80 and the short linkage 74 become alignedrelative to each other as shown in FIG. 5D, relatively little force isrequired by the hydraulic drive 86 to maintain the linkages in alignedrelationship. This is important since this is the relationship whichexists when the wheels 72 contact the ground.

After the axle 70 and the wheels 72 have reached the position shown inFIGS. 4B and 5D, the hydraulic drives 26 are operated to extend the rods30 from the cylinders 28. When this occurs, the hydraulic drives 26 andthe lift arms 34 pivot downwardly from the position shown in FIG. 4B tothe position shown in FIGS. 1 and 3. In this position, the wheels 72engage the ground. While the hydraulic drives 26 and the lift arms 34pivot downwardly, the trailing tag axle 70 and the wheels 72 remain inthe positions shown in FIGS. 4B and 5D.

With the wheels 72 contacting the ground, the dump truck 10 is able totravel along the road. As the dump truck 10 travels along the road, itmay encounter bumps rising from the road and dips (e.g. potholes)extending into the road. The arrangement shown in FIG. 11 compensatesfor these bumps and dips. This results from the pneumatic couplingbetween the rods 30 and the accumulator 48 through the conduits 44. Forexample, as the rods 30 extend from the cylinders 28, the gas (e.g.nitrogen) in the rods flows from the accumulator 48 through the conduits44 into the rods 30. Similarly, as the rods 30 move into the cylinders28, the gas returns to the accumulator 48 through the conduits 44. Inthis way, the trailing tag axle assembly 70 and the wheels 72 are ableto compensate in their movement for bumps and dips in the road. Thisprovides for a smooth movement of the dump truck 16 and the trailing tagaxle assembly 24 along the road. This results from the fact that theaccumulator 48 provides a large reservoir in comparison to the amount ofgas flowing into the rods. Thus, any pressure increases or decreases inthe accumulator 48 are minimized.

When it is desired to move the trailing tag axle 70 and the wheels 72from the operative position to the storage position, the hydraulicdrives 26 are initially operated to move the trailing tag axle and thewheels to the position above the dump body (FIG. 4B). The hydraulicdrives 26 and the lift arms 34 are then in the storage position. Thehydraulic drive 86 then sequences to move the trailing tag axle 70 andthe wheels 72 from the intermediate position shown in FIGS. 4B and 5D tothe storage position shown in FIGS. 4A and 5A.

FIG. 7 shows an arrangement for releasing the tailgate 20 so that thetailgate can be pivoted on the pin 22 as a fulcrum. In FIG. 7, anarrangement generally indicated at 100 shown is in broken lines in aposition in which the tailgate 20 is prevented from being opened. Thearrangement 100 is shown in solid lines in FIG. 7 in a position in whichthe tailgate 20 can be opened to provide for the dumping of the load inthe truck body 16 on the ground.

The arrangement 100 includes an actuator 102 with a hook 104 at one endfor engaging the bottom end of the tailgate 20. At its opposite end, theactuator 102 is pivotably attached to one end of a push rod 106 havingits other end coupled to a lever 108. The lever 108 is in turn pivotablycoupled to a pin 110 which extends into the frame. When the lever 108 isrotated on the pin 110, it causes the actuator 102 to move from theposition shown in broken lines in FIG. 7 as engaging the bottom of thetailgate to the position shown in solid lines in FIG. 7. In thisposition, the tailgate 20 is free to become opened for releasing theload in the truck body 16. The features shown in FIG. 7 and described inthis paragraph may be considered to be in the prior art. It is includedin this application to complete the disclosure.

FIG. 8 illustrates the electrical circuitry for moving the trailing tagaxle assembly 70 and the wheels 72 between the storage and operativepositions. FIG. 9 illustrates the hydraulic circuitry which operates inconjunction with the electrical circuitry shown in FIG. 8 to move thetrailing tag axle assembly 70 and the wheels between the storage andoperative positions. The construction and operation of the electricalcircuitry shown in FIG. 8 and the hydraulic circuitry shown in FIG. 9will be described in conjunction.

The circuitry shown in FIG. 8 includes two (2) switches which arerespectively designated as "Switch 1" and "Switch 2". These switches aredisposed on a control panel (not shown) in the cab 12 of the dump truck10. The Switch 1 is a three (3) position switch which can be locked ineach of the three (3) positions. These three (3) positions arerespectively labelled as "Up", "Neutral" and "Down". The Switch 2 isalso a three (3) position switch having its positions respectivelylabelled as "Manual", "Off" and "Auto". This switch is momentarilypositioned in the "Manual" position and is locked in the "Off" and"Auto" positions. The Switches 1 and 2 and a pressure gauge also mountedon the control panel in the cab 12 control the positioning of thetrailing tag axle assembly 70 and the wheels 72.

Assume that the trailing tag axle assembly 70 and the wheels 72 are inthe up or storage position. To lower the trailing tag axle 70 from thestorage position, the operator toggles switch 1 from the "Neutral"position to the "Down" position. Switch 2 is in the "Auto" position.This energizes solenoid valve #2 (SV2), solenoid valve #3 (SV3) andsolenoid valve #4 (SV4). Solenoid valve #2 (SV2) and solenoid valve #3(SV3) shift open and solenoid valve #4 (SV4) shifts closed. Solenoidvalve SV4 is a dump valve, dumping pump flow back to tank (T). The oilleaving the pump (P) then passes through solenoid valve SV2 and checkvalve #2 (CV2) in the free flow direction and out port C1 into port VAof the sequence valve. Oil now flows through port C1A and into the headend of the cylinder 92, causing the pistons 88 to extend and togglingthe wheels 72 into their operative position.

As the piston 88 is extending, the oil in the end of the piston 88 flowsinto the sequence valve through port C1B and through the check valve CV3in the free flow direction and out port VB and into port C2. The returnoil is blocked by check valve CV1, so it flows through SV3 back to tank(T). When the toggle piston 88 reaches the end of its stroke, thehydraulic pressure increases shifting the sequence valve on the C1A sideat a pressure of (1000 psi). This directs the oil into port C2A and intothe head end of the cylinders 28 in the hydraulic drives 26. Thepressure in the head ends of the cylinders 92 in the hydraulic drives 86remain at the sequence pressure (1000 psi). The lift pistons 30 extend.This causes the tag axle 70 to be lowered. The oil in the rod ends ofthe lift cylinder 28 flows into the dual sequence valve through port C2Band flows out port VB. The oil is blocked by check valve CV1 and passesthrough the solenoid valve SV3 on its way back to tank (T).

The lift cylinders 28 lower the trailing tag axle 70 until the wheels 72reach the ground. At this point, the pressure in the hydraulic circuit(and port S) begins to increase as the accumulator is pumped up. Theshuttle valve (LS1) is connected to both lines C1 and C2 and port S. Thepressure at port S will be the greater of the pressures in C1 or C2. Thepressure gauge and pressure switch (PS1) in the control box areconnected to the circuit through port S. The normally closed pressureswitch (PS1) keeps the solenoid valve SV4 energized. With the axle onthe ground, the accumulator 48 is pumped up to 1500 psi. The pressureswitch PS1 (set to open at 1500 psi) opens and de-energizes the solenoidvalve SV4. The normally open solenoid valve SV4 n row dumps the oil backto the tank T. The pressure switch PS1 has a detent such that thepressure switch PS1 will not close until the pressure drops to about1,200 psi. If the pressure drops somewhat, the solenoid valve SV4 willnot shift until the pressure drops below 1,200 psi. This keeps thehydraulic circuit from hunting.

The lift cylinders 92 not only operate the trailing tag axle 70 upwardlyand downwardly but they also serve as the suspension. This is well knownin the prior art. To accomplish this, the hollow rods 30 are chargedwith nitrogen. The pistons inside the rods 30 move back and forth insidethe rods. As the axle 70 moves upwardly and downwardly, the lift rods 30extend and contract inside the cylinders 28. The excess oil pushes thepistons 38 toward the end of the rods. Nitrogen gas trapped between thepistons 38 and the ends of the rods 30 compresses, allowing thisexpansion to occur.

The prior art has always had difficulty in either limiting the pressureincreases that occur as the gas is compressed between the pistons 38 andthe ends of the rods 30 to a reasonable amount or has had difficulty inobtaining enough throw of the suspension. Assuming that the temperatureof the gas remains substantially constant, the pressure increase isproportional to the volume decrease. Because of the limited volumeinside the rods 30 in the prior art and the amount of stroke in the liftcylinders 28 for which the accumulator 48 must compensate, the pressureincreases and thus the forces and stresses on the axle 70 have beensubstantial in the prior art. The accumulator 48 is also advantageousbecause the pressure of the fluid equalizes the pressure in liftcylinders 28. This results from the fact that the accumulator 48 isplumbed into the cylinders 30 at the opposite lateral ends of theaccumulator.

This invention continues the use of the pistons 38 inside the rod 30,but the gas side of the pistons 38 is connected to the large externalgas reservoir mounted inside the accumulator support tube 49. Thisallows the fast suspension action of the pistons 38. The large reservoircapacity of the accumulator 48 provides enough change in stroke of thelift rods 30 to permit the trailing tag axle 70 to drop into an eighteen(18) inch hole or move over a thirty six (36) inch bump while onlyincreasing the forces one and one half (1.5) times the normal operatingforce. If the trailing tag axle 70 tries to go higher than thirty six(36) inches, the relief valve (RV1) opens to protect against higherforces than the axle is designed to take.

To raise the trailing tag axle 70, the operator toggles the switch 1 inFIG. 8 from the down or neutral position to the up position. Thisenergizes the solenoid valve #1 (SV1), the solenoid valve #5 (SV5) anddeenergizes the solenoid valve #4 (SV4). The solenoid valves SV1 and SV5open and the solenoid valve SV4 closes. The oil leaving the pump (P)flows through the solenoid valve SV1, the check valve #1 (CV1) in thefree flow direction and out port C2 and then into the sequence valve 2through the port VB. From there the oil flows into the rod end of thelift cylinders 28 through the port C2B, causing the piston 30 to moveinto the cylinders 28 and raise the e tag axle 70. As the pistons 30move into the cylinders 28, the head end oil flows out through the portC2A, through the check valve in (CV4) in the free flow direction and outthe port VA and into the port C1. The return oil is blocked by the checkvalve CV2 and flows through the solenoid valve SV5 to the tank (T).

When the lift pistons 30 reach the end of their stroke, the hydraulicpressure increases until the sequence valve shifts at a pressure ofapproximately one thousand pounds per square inch (1000 psi) and directsthe oil into the port C1B and the rod end of the cylinder 92. Thepressure in the rod ends of the lift cylinders 28 remains at 1000 psi.As the piston 88 moves into the cylinder 92, the trailing tag axle 70 istoggled into its up or storage position as shown in FIGS. 4A and 5A. Asthe piston 88 moves into the cylinder 92, the head end oil flows throughthe port C1A and is dumped out of the port VA into the port C1 andpasses through the solenoid valve SV5 back to the tank (T).

Manual operation is used when the operator wants to put less load on thetrailing axle assembly 24 than the maximum. In the "auto" mode, currentis always provided to the pressure switch PS1. When the pressure comesup to 1500 psi, the pressure switch PS1 opens. In the manual mode, theoperator pushes the momentary switch 2 to manual. This energizes thesolenoid valve SV4. The operator watches the pressure gauge in the cabuntil the trailing axle is pressured up to the desired pressure. Theoperator then releases the momentary switch 2 which returns to the "Off"position. In this manner, the operator can set the pressure at thetrailing axle assembly 24 to whatever is required less than the maximumwhich is controlled by the pressure switch PS1.

The trailing tag axle assembly 24 has certain important advantages. Itprovides for the attachment of the trailing tag axle assembly 28 to theside panels 18 of the dump truck 10 without bowing the frame 14 awayfrom the truck body. It provides for the full use of the distancebetween the rear wheels 98 of the dump truck 10 and the wheels 72 in thetrailing tag axle assembly in distributing the weight of the load in thetruck body 16 between the front wheels on the dump truck 10 and thewheels 72. It provides for a smooth and efficient movement of the tagaxle assembly 24 over bumps and dips such as potholes in the road whenthe trailing tag axle assembly is in the operative position with thewheels 72 on the road and when the dump truck 10 is travelling along theroad. When the wheels 72 move over bumps or into dips in the road, thechanges in force are limited because of the large reservoir provided bythe accumulator 48. This tends to assure long life in the operation ofthe trailing axle assembly 24.

The trailing tag axle assembly 24 minimizes the height of the trailingtag axle assembly above the ground when the tag axle assembly is in thestorage position. It also provides for the dumping of the load in thetruck body 16 without any obstruction from the trailing tag axleassembly when the trailing tag axle assembly is in the storage position.The trailing tag axle assembly 24 is also advantageous because it canbalance uneven loads on the opposite lateral sides of the truck bodywhen the trailing tag axle assembly is in the operative position on theground. This results from the balancing action of the gas in theaccumulator 48.

Although this invention has been disclosed and illustrated withreference to particular embodiments, the principles involved aresusceptible for use in numerous other embodiments which will be apparentto persons skilled in the art. The invention is, therefore, to belimited only as indicated by the scope of the appended claims.

What is claimed is:
 1. An improved combination trailing axle assembly and dump vehicle of the type having a dump body with a floor and side walls and a load discharge area at one end thereof, the improvement comprising:means for attaching said assembly to an exterior portion of said dump body other than a tailgate thereof without constricting said load discharge area, and means for re-positioning said assembly from a load-bearing position to a non-load-bearing possition substantially above said load discharge area, whereby said dump vehicle may discharge its load without obstruction by said assembly.
 2. The improved combination of claim 1, wherein s aid re-positioning means are substantially aligned with the side walls of said dump body.
 3. The improved combination of claim 2, wherein said re-positioning means comprises hydraulic means for effecting said re-positioning.
 4. The improved combination of claim 2, wherein said re-positioning means comprises pneumatic means for effecting said re-positioning.
 5. The improved combination of claim 1, said side walls further comprising reinforcements substantially surrounding one end thereof.
 6. The improved combination of claim 5, wherein said attaching means further comprises means for attaching said assembly to a portion of said side wall reinforcements.
 7. The improved combination of claim 1, said trailing axle assembly further comprising an axle portion thereof with wheels and tires thereon and means for rotating said axle portion to a position whereby at least a portion of said tires are positioned at least partially forward of said load discharge area.
 8. The improved combination of claim 7, said dump body further comprising side wall reinforcements supporting said trailing axle assembly and said axle portion rotation means being substantially aligned with said side walls of said dump body. 